Reland: Fix crash when the source browser window is deleted during a drag

ui/views/widget/desktop_aura/desktop_drag_drop_client_win.h

Index: ui/views/widget/desktop_aura/desktop_drag_drop_client_win.h
diff --git a/ui/views/widget/desktop_aura/desktop_drag_drop_client_win.h b/ui/views/widget/desktop_aura/desktop_drag_drop_client_win.h
index 0da14e008cd1ba484b4dba85bdd509b5491d5853..36bcc7364d65b74168813ddb017d7e70574319a7 100644
--- a/ui/views/widget/desktop_aura/desktop_drag_drop_client_win.h
+++ b/ui/views/widget/desktop_aura/desktop_drag_drop_client_win.h
@@ -7,6 +7,7 @@
 
 #include "base/compiler_specific.h"
 #include "base/memory/ref_counted.h"
+#include "base/memory/weak_ptr.h"
 #include "ui/views/views_export.h"
 #include "ui/wm/public/drag_drop_client.h"
 
@@ -49,6 +50,8 @@ class VIEWS_EXPORT DesktopDragDropClientWin
 
   scoped_refptr<DesktopDropTargetWin> drop_target_;
 
+  base::WeakPtrFactory<DesktopDragDropClientWin> weak_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(DesktopDragDropClientWin);
 };